In recent magnetic disk devices, an inductive thin film head for recording data and a magnetic head element for reproducing data are provided, and the linear density and track density have been increased to improve areal recording density. A magnetoresistive head and a spin valve head have been proposed as the data reproducing magnetic head element in order to achieve such increases in recording density.
For example, a magnetic head mounted with a magnetoresistive head element comprises, as is illustrated by FIG. 9, a reproducing head 83 that is a magnetoresistive head element and a recording head 81 that is the inductive thin film head element and these are separated by a magnetic shield 84 and laminated.
The reproducing head includes the magnetoresistive head element (MR element) that is sandwiched by the magnetic shields 84, a sensor part 86, a pair of electrodes 89 for flowing sensing current through the sensor part 86 and a pair of permanent magnets 85 for reducing the Barkhausen noise of the MR element. The data is reproduced by moving the magnetic disk with respect to the head so that a sensing current flows through sensor part 86 from the pair of the electrodes 89. Very small changes in the magnetic field signals on the
magnetic disk are detectable through the resistance changes of the sensor part 86.
The sensor part includes several layers, as is illustrated by FIG. 1A. In the figure, a layer 51 is the magnetoresistive element. A transverse bias layer 54 is a soft adjacent layer (SAL) that applies a transverse bias to the MR layer 51. A spacer layer 53 magnetically separates the transverse layer 54 and the MR layer 51. Also, an under part gap layer 55 and an under part shield layer 56 are arranged under the transverse bias layer 54.
The principal component of the spacer layer 53 is Ta, which is used as the principal component since it provides for preferred orientation of the crystals of the MR element 51. The under part shield layer 56 corresponds to shield 84 as shown in FIG. 9. The under part shield layers described hereinafter correspond to similar components as these.
The magnetoresistive head element operates based on the anisotropic magnetoresistive (AMR) effect wherein the resistance of the MR layer 51 changes in proportion to the square of the cosine of an angle between the direction of the magnetization of the MR layer 51 and the direction of the sense current. The MR head element (hereinafter, MR head) outputs a signal utilizing the change in resistance in the MR element through which the sense current flows in a constant direction, based on the characteristic that the magnetization and the resistance of the MR head changes due to the change in magnetic field from the magnetic recording media.
Therefore, the MR layer should have an excellent soft-magnetic property in order to obtain a large AMR effect for the head with low noise and high output level. For the MR layer, an alloy layer of Co, Fe and Ni is used and an NiFe alloy is preferred since it has a superior soft-magnetic property.
To improve the soft-magnetic property of the NiFe alloy, as is illustrated by FIG. 1A, the spacer layer 53, of which the principal component is Ta, is arranged on the transverse bias layer 54. The reason Ta is used as the principal component for the spacer layer 53 is that it is easier to obtain proper orientation of the crystals of the layer 51, which is essentially NiFe, than it is with any other materials.
In another prior art head arrangement, as illustrated by FIG. 1B, the order of the layers is inverted with respect to the under part gap layer 55 and the under part shield layer 56. In particular, the figure shows an order in which the transverse bias layer 61, a spacer layer 53 which is essentially of Ta, an MR layer 51 and an underlayer 65 which is essentially of Ta, are arranged on the under part gap layer 55 and the under part shield layer 56. Under layer 65 is provided to help the orientation of the crystals of MR layer 51.
Recently, a spin valve (SV) head has been developed as a reproducing head for attaining a higher recording density that has a giant magnetoresistive (GMR) effect. A GMR head can output a larger signal as compared with an MR head.
As shown in FIG. 2, only the sensor part of the structure of the SV head is different from that of the MR head. The sensor part of the SV head has a structure in which between pinned layer 72 and free layer 74, which are made of a ferromagnetic material such as NiFe, is a nonmagnetic layer 73 that is made of a metallic, nonmagnetic material, such as Cu.
In an SV head, the resistance changes in proportion to the cosine of the angle between the directions of the magnetization of the pinned layer 72 and the free layer 74. To obtain a linear output, it is necessary for the direction of the magnetization of the pinned layer 72 to be fixed by the adjoining antiferromagnetic layer 71, which is essentially FeMn. Also, the direction of the magnetization of the free layer 74 must be perpendicular to the direction of the magnetization of the pinned layer at the biased state.
In an SV head, the free layer 74 is required to be of a high quality soft-magnetic material layer for outputting signals with the rotation of magnetization corresponding to the magnetic signal field from the magnetic disk. Accordingly, the free layer of the SV head, similar to the case for the MR head uses an NiFe layer with a Ta underlayer. The free layer 74 is not limited to the single layer of the NiFe material, however, and a two-layer structure of a CoFe layer on a NiFe layer can also be used.
In the manufacturing process of the SV head, two steps or more of heat treatments in a magnetic field are necessary. These heat treatment steps are for ensuring that the directions of magnetization between the free layer 74 and the pinned layer 72 are perpendicular to one another. In particular, one of the heat treatments is for the magnetic polarization of the free layer 74, during which the direction of an applied magnetic field is set to be along the easy axis of magnetization of the free layer. The other heat treatment is for the magnetic polarization of the pinned layer 72, during which the direction of the applied magnetic field is set perpendicular to the easy axis of the magnetization of the free layer 74.
Thus, the free layer of the SV head is heat treated twice or more under the application of an applied magnetic field in a direction along the easy axis of magnetization of the free layer and in a direction perpendicular to it. To obtain an SV head with low noise levels, the angular dispersion of the magnetic anisotropy of the free layer must be kept to a minimum after the heat treatments.
Further, the MR layer or free layer must be made as thin as possible to obtain high sensitivity, which can be achieved by any suitable technique, such as by sputtering. The preferred thickness for the MR layer is about 10 to 15 nm and for the free layer of the SV head is about 5 to 10 nm of the soft ferromagnetic material, such as NiFe.
Although the SV head has been described generally with reference to FIG. 2, its construction is well known from the prior art, for example as described in Japanese patent publication 4-358310.